CUCM 8.6 Software MTP G711alaw to G711ulaw

[James Hawkins]

Hello,

I have a customer that uses CUCM 8.6 and UCCX 8.5.

The system in the UK and uses SIP trunks via 2921 CUBEs for PSTN access.

The SIP provider sends using G711alaw and the CUBEs transcode to G711ulaw before sending the calls to CUCM, UCCX etc.

The reason for doing this is that UCCX does not support G711alaw.

This has been working ok for about six months but recently the CUBEs have started misbehaving and TAC seem to think it is a bug (CSCuh27343
) which is present in all versions of software and will not be fixed until 15.3(3)M1 is released at the end of the month.

I am wondering whether it is possible to use the CUCM software MTP feature to convert between G711alaw and G711ulaw instead of the CUBE PVDM3 DSPs.

Has anyone done this? - if yes how well did it work?

[Manish Gogna · Accepted solution]

Hi James,

It can be done using sofware MTP but there are capacity considerations as the RTP will flow through the server. A dedicated server might be needed in case the call volume is high. Also, i have read somewhere that in case of an RTP packet loss the MTP in CUCM repairs the RTP flow by inserting an empty RTP packet into the RTP flow  in place of absent packet, which may cause issues in certain call flows.

HTH

Manish

[James Hawkins]

Hi Manish,

Thank you for answering this for me. I think we can both agree that this would not be an ideal solution but it is good to know that it is an option.

The customer only has 140 phones with a maximum of 40 calls through the CUBE (normally less than 20) and has two 1 vCPU Subscribers that run the software MTP service so I guess that this would be acceptable.

The customer actually has two CUBEs and only one is failing so I may try reconfiguring the dodgy one to use the software MTP overnight.

Thank you very much for your help.

James

[Ayodeji Okanlawon]

James,

Depending on the IOS you are running, you can also use a xcoder for this. I belive with IOS 15.0 and above a xcoder can xcode between G711a/G711ulaw...Just another option to consider if the MTP is an issue

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[James Hawkins]

Hi,

Thanks for the response. I am actually using the Local Transoding Interface feature on the CUBE at the moment. The problems I am having with the CUBE happen with transcoded calls so I was looking at options to move the codec conversion to another device.

The customer does not have any other gateways with PVDMs available (other than an identical 2921 also acting as a CUBE) so I was looking at other ways to do the conversion.

I have spoken to the ITSP and they can actually change the codec on the external call legs to G711ulaw so I guess that might be the simplest option.

Thanks

[Ayodeji Okanlawon]

Thanks for the feedback. Changing the codec from the provider is absolutely the best option. It shouldnt be so difficult, otherwise come to us (Verizon broadsoft) and we will give you any codec you want

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"opportunity is a haughty goddess who waste no time with those who are unprepared"